The reactions between electroless Ni-Cu-P Deposit and 63Sn-37Pb flip chip solder bumps during reflow

Abstract

This study investigates the interfacial reactions between electroless Ni-Cu-P deposit and 63Sn-37Pb solder bumps under various reflow conditions. The morphology of the intermetallic compounds formed at the Ni-Cu-P/Sn-Pb interface changes with respect to reflow cycle, reflow temperature, and reflow time. The (Ni,Cu) 3 Sn 4 compounds with three different morphologies of fine grain, whisker, and polygonal grain form at the Ni-Cu-P/Sn-Pb interface after reflow at 220°C for 15 s. The whisker-shape and polygonal grains detach from the NiCu-P deposit into the Sn-Pb solder during multiple reflows. The (Ni,Cu) 3 Sn 4 compound grows rapidly when the reflow temperature is above the Ni-Sn eutectic temperature, 231°C. A continuous (Ni,Cu) 3 Sn 4 layer forms after reflow at 220°C for 10 min. A 4.5 µm Ni-Cu-P deposit prevents the interdiffusion of Sn and Al atoms across the Ni-Cu-P deposit after 10 reflow cycles at 220°C for 15 s and after reflow at 220°C for 10 min.

Development of lead-free Sn–0.7Cu/Al2O3nanocomposite solders with superior strength

“…Recently, the development of new processing techniques in the electronic assembly industry has been accelerated in order to cope with the requirements arising from the switch to leadfree solders. Solid state bonding techniques, for example, thermal compression and thermosonic processes, which can be integrated into electronic assembly and packaging facilities, are already in industrial practice and under rapid development for interconnect applications [13][14][15]. Since there is no melting required in the solid state bonding, the segregation of reinforcement particles which restricted the industrial applications of composite solders is not an issue any more.…”